grounded
You would still potentially still be left looking for the haystack, let alone the needle.
Personally, I think the most important change would be to mandate aircraft reporting their position by satellite every 2 minuetes or so, not for ATC purposes per se, but for quick location purposes in SAR instances like this. This function should be independent and isolated from the flight crew, so they can not shut it down. It should probably be on a separate bus and backed up by battery and should report any power loss from the main busses. The battery should have sufficient storage capacity to maintain transmissions for the maximum endurance of the type.